This invention relates to a burner of the same general type as disclosed in Spielman et al U.S. Pat. No. 3,418,060. In such a burner, gas and combustion air are delivered into a burner body and are ignited upon passing from the body and into a tubular burner block. An inwardly coverging nozzle is provided at the discharge end of the burner block and serves to radially contract the advancing stream of gas and air to promote efficient final combustion and to cause the flame to be discharged from the burner at a high velocity. Such a burner has experienced significant commercial success in recent years and is widely referred to as a high velocity burner.